Merge pull request #59 from pipermerriam/piper/fix-how-empty-response…

…s-are-handled

change populus handling of empty responses to function calls

populus/contracts/common.py

@@ -6,6 +6,14 @@
 )
 
 
+class EmptyDataError(Exception):
+    """
+    Raised when a call to a function unexpectedly returns empty data `0x` when
+    a response was expected.
+    """
+    pass
+
+
 class ContractBound(object):
     _contract = None
 
@@ -60,7 +68,13 @@ def output_types(self):
 
     def cast_return_data(self, outputs):
         if len(self.output_types) != 1:
-            return decode_multi(self.output_types, outputs)
+            try:
+                return decode_multi(self.output_types, outputs)
+            except AssertionError:
+                raise EmptyDataError("call to {0} unexpectedly returned no data".format(self))
         output_type = self.output_types[0]
 
-        return decode_single(output_type, outputs)
+        try:
+            return decode_single(output_type, outputs)
+        except AssertionError:
+            raise EmptyDataError("call to {0} unexpectedly returned no data".format(self))

populus/contracts/utils.py

@@ -8,9 +8,10 @@
 def decode_single(typ, data):
     base, sub, _ = abi.process_type(typ)
 
+    # ensure that we aren't trying to decode an empty response.
+    assert len(data) > 2
+
     if base == 'address':
-        if data == "0x":
-            return "0x" + "0" * 40
         return '0x' + strip_0x_prefix(data[-40:])
     elif base == 'string' or base == 'bytes' or base == 'hash':
         if sub:

tests/contracts/test_decode_multi.py

@@ -15,6 +15,11 @@ def test_decode_two_uint32(input, expected):
     assert output == expected
 
 
+def test_empty_data_raises():
+    with pytest.raises(AssertionError):
+        decode_multi(['uint32', 'uint32'], '0x')
+
+
 def test_decode_various():
     data = ('0x00000000000000000000000082a978b3f5962a5b0957d9ee9eef472ee55b42f10000000000000'
             '0000000000000000000000000000000000000000000000000017374757069642070696e6b20616e69'

tests/contracts/test_decode_single_type.py

@@ -76,10 +76,6 @@ def test_decode_bytes():
 @pytest.mark.parametrize(
     'input,expected',
     (
-        (
-            '0x',
-            '0x0000000000000000000000000000000000000000',
-        ),
         (
             '0x0000000000000000000000000000000000000000000000000000000000000000',
             '0x0000000000000000000000000000000000000000',
@@ -105,3 +101,9 @@ def test_decode_bytes():
 def test_decode_address(input, expected):
     output = decode_single('address', input)
     assert output == expected
+
+
+@pytest.mark.parametrize('_type', ('address', 'bytes32', 'uint256', 'int256', 'bool'))
+def test_raises_on_empty_data(_type):
+    with pytest.raises(AssertionError):
+        decode_single(_type, '0x')